Coverage analysis tool for optical data¶
Module using the sepal_ui framework and an interactive Voila dashboard to create maps of cloud-free observations for major optical satellites as available on Google’s Earth Engine Platform.
The framework follows the logic of bfasts’ countObs and summaryBrick functions as described [here](http://www.loicdutrieux.net/bfastSpatial/#Data_Inventory).
For bfast specific requirements check [Schultz et al. 2013](http://dx.doi.org/10.1109/JSTARS.2015.2477473) for further background.
The process is done in 3 steps described in the below sections:
Select an AOI¶
Using the provided AOI selector, select an AOI of your choice between the different methods available in the tool. We provide 3 administration descriptions (from level 0 to 2) and 3 custom shapes (drawn directly on the map, asset or shapefile).
If a custom aoi from shape or drawing is selected, you will be able to use it directly and the upload to GEE will be launched in the background
Select dataset parameters¶
To perform the bfast preanalysis you need to provide the tool with key parameters:
date range: The start and end date of your analysis
sensors: The list of sensors you want to use (Landsat missions & Sentinel-2)
Tier 2: Tier 2 images of the Landsat missions (this might lead to wrong results)
SR: whether to use Surface Reflectance images (SR). default to Top of atmosphere (TOA)
Once all your parameters are selected you need to click on the button to make your selection effective
After having selected your parameters you can move to the Visualization tile. Select one of the statistical measures to display in the following list:
Cloud-free pixel count
Total pixel count (i.e. scene coverage)
NDVI Std. Dev.
You can also decide to produce stats on yearly basis using the provided switch
The image will be dynamically re-evaluated and re-centered on every change
Once you’re happy with the information displayed then can be exported to be further used in a GIS software or in a GEE process. The tool provides 2 main exportation options, as an asset(in GEE) or as a Tif file in SEPAL.
Both use the GEE export system and share the same set of parameter:
statistical measures to export
count of cloud-free observation per pixel
NDVI’s median of cloud-free observations
NDVI's std. dev. of cloud-free observations
count for all observations per pixel
full timespan calculation(s)
scale: the resolution (in meters) to us in GEE exported file
When the image is exported to SEPAL, you cannot quit the application until the downloading is finished.